Hard non-oxide or oxide ceramic materials are commonly used in applications requiring materials with a high hardness, superior strength, good corrosion resistance, and high thermal conductivity, such as the materials used in acidic, caustic, corrosive, abrasive, high speed, or high temperature environments. These types of applications include rotating equipment, pump seals and bearings, gas turbine components, mixing nozzles, and flame holders. Examples of these hard non-oxide or oxide ceramic materials include but are not limited to silicon carbide, pressureless sintered silicon carbide, liquid phase sintered silicon carbide, reaction bonded silicon carbide, tungsten carbide, aluminum oxide, and silicon nitride.
A drawback to these hard non-oxide or oxide ceramic materials is the lack of self-lubricity when used alone. A self-lubricating solid is one having low friction in the absence of an adequate lubricant. For example, in applications having a high PV (pressure-sliding velocity) or marginal lubrication conditions, parts, such as seals or bearings, having a hard non-oxide or oxide ceramic material surface adjoining with relative motion against another surface made of the same or other hard non-oxide or oxide ceramic material, other silicon carbide materials, other ceramics, or steel will wear excessively due to the forces generated by the high friction. In marginal lubrication conditions with mating surfaces, special wear surfaces must be provided on at least one of the bodies.
Graphite is a known lubricant and has been incorporated into carbon and silicon carbide materials to impart a self-lubricating property to the material. For example, U.S. Pat. Nos. 5,580,834, 5,656,563, and 5,968,653, the contents of which are incorporated herein by reference, teach the use of a carbon graphite/silicon carbide composite material. Other inclusions, such as tribology enhancing additives, porosity, boron carbide, etc., can also improve the tribology of the material. The composite materials have wear resistance superior to hard non-oxide or oxide ceramic materials, in that the material of the present invention can run against itself or other hard non-oxide or oxide ceramic, non-self-lubricating materials in sliding face applications, such as for mechanical seals and pump bearings, in marginal lubrication conditions. Composite materials also have thermal shock resistance superior to hard non-oxide or oxide ceramic materials. In catastrophic failure or dry run conditions, such as when fluid is lost in pump applications, seals and bearings made of the composite material have enhanced survivability and can maintain their integrity, while seals and bearings made of hard non-oxide or oxide ceramic materials can fail almost immediately. However, a drawback to the use of composite materials alone is that the composite material does not exhibit the same level of superior hardness, corrosion resistance, thermal conductivity, and strength that are enhanced physical properties of hard non-oxide or oxide ceramic materials.
Accordingly, there is a need to combine the superior physical properties of hard non-oxide or oxide ceramic materials with the enhanced tribological capability of composite versions of these hard non-oxide or oxide ceramic materials.